Electrical switching circuit



Nov. 5, 1968 L. A. CHAVIS 3,408,993

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INVENTOR. Leo/v 9. CH9 v/S UiZ5on,Se1/: Ze McKinnon HTT'OENEKj United States Patent 3,408,993 ELECTRICAL SWITCHING CIRCUIT Leon A. Chavis, Detroit, Mich., assignor to Mallory Electric Corporation, Detroit, Mich., a corporation of Michigan Filed Apr. 9, 1965, Ser. No. 447,004 3 Claims. (Cl. 123-148) ABSTRACT OF THE DISCLOSURE The electrical switching circuit is for use as a vehicle ignition system. The ignition system employs solid state components and an improvement in switching circuits which reduces the necessity for exact control of the dwell time of the points or other timing device utilized in the ignition system.

The circuit comprises a step-up transformer which has the usual primary and secondary winding. The anodecathode circuit of a gate controlled switch is placed in series with the primary winding to permit current flow through this Winding when the switch is conducting. The positive side of a DC. power source is connected to the gate of the switch for making the gate positive with respect to the cathode. A parallel arranged resistor and capacitor are connected between the gate and the power source. Means are provided for repetitively establishing a potential on the power source side of the capacitor which is less than the potential on the opposite side of the capacitor. This results in the step of making the gate negative with respect to the cathode. This causes the switch to ease conducting for a period determined by the RC time constant of the resistor and capacitor.

Background of the invention Conventional electric vehicle ignition systems have, in the past, comprised a circuit breaker and capacitor circuit which have served to directly open and close the connection to a DC power source of the primary coil of a step-up transformer. Such transformers, upon the opening of the primary coil circuit with the resultant collapse in the magnetic field, generate a very high voltage in the secondary coil which serves to cause a spark in the spark plug to ignite a combustible mixture. Recently, such conventional ignition systems have been modified for many applications by the use of solid state devices in switching circuits to trigger the transformer. The advantage of such modification has resided in better performance of the ignition system and an improved reliability and durability of the ignition system.

The present invention constitutes an improvement over previous ignition systems employing solid state components in that the point of closure and dwell time of the contacts or other timing device is not critical and does not alfect performance of the system.

It is, therefore, an object of this invention to provide an electrical vehicle ignition system employing solid state components in connection with a timing circuit wherein the point of closure of the timing circuit and dwell time of closure of the timing circuit is not critical.

A further object of the invention is to provide a solid state component for controlling the passage of current through the primary coil of an ignition transformer, said solid state component being capable of being returned to the off state when a negative signal is applied to the gate with respect to the cathode.

A further object of the invention is to provide an R-C circuit which is capable of applying to the above-mentioned solid state device a negative signal to the gate 'with respect to the cathode for an exactly predetermined pc- 3 ,408,993 Patented Nov. 5, 1968 riod of timeto thereby. control the periods. of time when current is not flowing through the primary windingof the transformer.

A still further object of. the invention is to provide a conventional transistor which is energized and deenergized by opening andclosing of the timing device, .energization of the transistor functioningto actuate the R.-C circuit for turning the solid state device to the off condition for a predetermined time.

Other objects of this invention will appear in the following description and appended claims, reference-being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

In the drawings:

FIGURE 1 is a schematic view of one embodiment of the vehicle ignition system in accordance with the present invention; and

FIGURE 2 is a graph of the building up and collapse of the magnetic field of the ignition system.

Before explaining the present invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and arrange ment of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

Referring to FIGURE 1, it will be noted that a DC vehicle battery 10 has the negative terminal grounded at 12. A lead 14 extends from the positive terminal. An ignition switch 16 is provided in lead 14 for turning the ignition system on and off.

Lead 14 is connected to one side of the primary winding 18 of a voltage step-up transformer 20. The other side of the primary winding 18 is connected to the anode of a gate controlled switch 24 by lead 26. The cathode of the gate controlled switch is grounded at 28. A resistor 30 is connected between leads 14 and 32 by a lead 34. The lead 32 is connected to the gate of the gate controlled switch.

A gate controlled switch is a 4-layer semi-conductor device having three p-n junctions and three external connections, the anode, cathode and gate. The middle n-region is the high-resistivity basic starting silicone material. The two p-regions are normally diffused, and the n+-region (cathode) can be either diffused or alloyed. The gate and cathode are analogous to the base and emitter of a conventional transistor; however, the anode can not be compared to the transistor collector because it is in reality another emitter.

The characteristics of a gate controlled switch are similar to those of a conventional silicone controlled rectifier. The device is triggered on by applying a positive gate signal with respect to the cathode. Once turned on, it will remain on until a negative signal is applied to the gate with respect to the cathode, which turns it off.

Consequently, it will be appreciated that when the ignition switch 16 is closed, a positive signal will be applied to the gate with respect to the grounded cathode. This positive signal will turn the gate controlled switch to the on condition whereupon current will flow through the primary winding 18. Flow of current through the primary winding will result in creation of a magnetic field for inducing a high voltage in the secondary winding 36. It will be noted that one side of the secondary Winding 36 is connected to the high voltage vehicle distributor (not shown) via lead 38.

One end of the primary and secondary windings are connected together by lead 40. A conventional silicon diode 42 has one side grounded and is connected to the lead 40 via lead 44. The diode 42 functions to limit any negative voltage excursions to ground potential which may be developed by the step-up transformer 20. This transformer may have a turns ratio of from 60 to 1 to 300 to 1 and the provision of diode 42 is thus an etfective protective measure.

Another lead 46 extends from lead 40 to ground. A capacitor 48 is provided in lead 46. The capacitor 48 also functions to reduce the effects of the back EMF of the step-up transformer 20.

It will be appreciated from the foregoing description that means have been described for energizing the transformer 20. The remaining portion of the circuit is provided to deenergize the transformer to cause collapse of the magnetic field at repetitive intervals to thus induce a high voltage in the secondary winding 36 sufficient to cause a spark to be generated in the vehicle spark plugs.

This portion of the circuit includes a lead 50 which extends from lead 14 from a point behind the switch 16. A resistor 52 is provided in lead 50. A current-interrupting device 54 is also provided in lead 50. The currentinterrupting device 54 is illustrated as the conventional ignition breaker points. However, any current-interrupting device may be used. The requirement for the device is that it sense the mechanical rotation of the spark-ignited combustion engine. A magnetic device which produces a pulse to indicate the piston position in respect to the time that a spark must occur for proper engine operation might also be used or a photo-electric device which produces a pulse at a specific time when the spark must occur for proper engine operation might also be employed. The lead 50 is grounded at 56.

A lead 58 extends from the lead 50 from a point between the current-interrupting device 54 and resistor 52. The lead 58 extends to the base of a conventional transistor 60. The transistor 60 may be of the pnp or npn type. The emitter of the transistor is grounded at 62. The collector is connected to the lead 32. Also connected to the collector is a lead 64 which extends from the lead 14. A resistor 66 is provided in lead 64. A capacitor 68 is provided in the lead 32 between the point of connection of the leads 64, 34.

In operation, when the current-interrupting device 54 is open as illustrated, the transistor 60 is turned on. The proper bias for the base is set by the values of the resistor 52, 61. When the device 54 is closed, transistor 60 will cease to conduct because, in eltect, closing of the device 54 results in a shunt around the transistor.

When transistor 60 is not conducting, the capacitor 68 is charged. The voltage drop across the capacitor is substantially equal to the voltage drop across resistor 30. The side 70 of the capacitor is negative with respect to the side 72.

When the transistor 60 conducts, current flows through lead 64, resistor 66, through the collector-emitter circuit of the transistor and thence to ground. As soon as the transistor is driven to saturation, which for the purposes of the present invention may be considered to be instantaneous, the collector will reach ground potential. The side 72 of the capacitor 68 will thus be at ground potential, placing the gate of the gate controlled switch 24 at the negative potential of the capacitor, this being equal to the voltage drop across the capacitor. The gate of the switch 24 is thus negative with respect to the cathode, resulting in turning 011 of the switch 24.

As soon as the switch 24 is turned oif, current will cease to flow through the primary winding 18 and the magnetic field will collapse, resulting in an induced voltage in the secondary winding 36 sufficient to cause sparking. The switch 24 will remain turned off for a period of time determined by the R-C time constant of the resistor 30 and capacitor 68. The capacitor 68 will, of course, begin to charge to the battery voltage through the resistor 30 as soon as the transistor 60 begins to conduct The time necessary for this to occur is set so that a voltage of sufficient value will have been developed in the secondary winding 36 for sparking purposes. As soon as the side 70 of the capacitor 68 becomes positive with respect to the cathode of the switch 24, the switch 24 will again begin conducting. The current-interrupting device 54 is opened at some point after sparking has occurred and before the next spark is needed. It will be appreciated, however, that the point of opening of the device 54 does not effect or control the point at which current again begins to flow through the primary winding 18.

FIGURE 2 illustrates the time factors involved in the present ignition system. Two cycles of the building up and collapsing of the magnetic field in the transformer 20 are illustrated. Current begins to flow through the primary winding 18 at point A. As above discussed, this is determined by the R-C constant of the resistor 30 and capacitor 68. The field is fully developed at point B. The field is maintained for a short interval of time and at point C, which is the opening of current-interrupting device 54, the field begins to collapse and is completely collapsed at point D. The field remains collapsed for a time interval until current again flows through primary winding 18 at point A. The current-interrupting device 54 is opened at a time between points A and C. Of course, it must be opened some time before point C in order to reestablish the charge on capacitor 68.

It will be appreciated that the curve shown does not conform to the specific configuration of a curve which would be encountered in practice. The curve shown is merely designed to illustrate the time and event happenings in the circuit.

The circuit as thus described is advantageous over conventional circuits in that it is not necessary to provide the usual by-pass relay to provide the maximum voltage in the transformer 20. In essence, building up of the field in the transformer 20 occurs automatically and is not dependent upon the point of opening of the device 54. Additionally, the device 54 does not carry large current. This improves point life.

Having thus described my invention, I claim:

1. An ignition system for an internal combustion engine comprising a step-up transformer having a primary winding and a secondary winding, a gate controlled switch, the anode-cathode circuit of said switch being in series with said primary winding for permitting current flow through the primary winding when the switch is conducting, a DC power source, the positive side of said power source being connected to the gate of said switch for making the gate positive with respect to the cathode, a parallel arranged resistor and capacitor between the gate and said power source, means for repetitively establishing a potential on the power source side of the capacitor which is less than the potential on the opposite side thereof to thereby make the gate negative with respect to the cathode to cause the gate controlled switch to cease conducting for a period determined by the R-C time constant of said resistor and capacitor.

2. An ignition system for an internal combustion engine comprising a step-up transformer having a primary winding and a secondary winding, a gate controlled switch, the anode-cathode circuit of said switch being in series with said primary winding for permitting current flow through the primary winding when the switch is conducting, a DC power source, the positive side of said power source being connected to the gate of said switch for making the gate positive with respect to the cathode, an R-C circuit comprising a first resistor in parallel with a series arranged second resistor and capacitor, said R-C circuit being connected between the gate and said power source, a transistor having an emitter, collector and base, the emitter-collector circuit being connected to the R-C circuit at a point between the second resistor and capacitor, switch means for repetitively biasing the transistor to a conducting and non-conducting state. conduction of said transistor establishing a potential on the power source side of the capaictor which is less than the potential on the opposite side thereof to thereby make the gate of the gate controlled switch negative with respect to the cathode to cause the gate controlled switch to cease conducting for a period determined by the R-C time constant of said first resistor and capacitor.

3. An ignition system for an internal combustion engine comprising a step-up transformer having a primary winding and a secondary winding, a gate controlled switch having an anode, cathode and gate, the anode of said switch being in series with said primary winding, the cathode of said switch being grounded, the anode-cathode circuit of said switch permitting current fiow through the primary winding when the switch is conducting, a DC power source, the positive side of the power source being connected to the gate of said switch for making the gate positive with respect to the cathode, an R-C circuit comprising a first resistor in parallel with a series arranged second resistor and capacitor, said R-C circuit being connected between the gate and said power source, a transistor having an emitter, collector and base, the collector being connected to the R-C circuit at a point between the second resistor and capacitor, the emitter being connected to ground, the positive side of the power source being connected to the base of said resistor, bias resistor means between the positive side of the power source and said base to efiect a voltage bias to cause said transistor to conduct switch means for repetitively biasing the transistor to a conducting and non-conducting state, said switch means being connected between at least a portion of said bias resistor means and the positive side of said power source and ground, closure of said switch means being elfective to reduce the transistor voltage bias to bias the transistor to the nonconducting state, conduction of the said transistor establishing a potential on the power source side of the capacitor which is less than the potential on the opposite side thereof to thereby make the gate of the gate controlled switch negative with respect to the cathode to cause the gate cont-rolled switch to cease conducting for a period determined by the RC time constant of said first resistor and capacitor.

References Cited UNITED STATES PATENTS 3,087,001 4/1963 Short et al. 3,087,090 4/ 1963 Konopa. 3,237,620 3/1966 Hetzler et al. 3,260,251 7/1966 Lange.

3,291,110 12/ 1966 Peters.

3,319,617 5/1967 Gilbert. 3,320,939 5/ 1967 Huntzinger et al.

LAURENCE M. GOODRIDGE, Primary Examiner. 

